Gene therapy is a treatment utilized to treat diseases such as varieties of cancers, cystic fibrosis, Parkinson's disease, Alzheimer's disease, and AIDS. Gene therapy operates by transferring genetic material to target cells. Although a promising therapeutic strategy, gene therapy is limited by toxicity and efficiency of gene delivery systems.
Polyamines are used in many areas of materials engineering (such as detergents, water treatment agents, and cosmetics) with applications ranging from biomedicine to structural resins. One class of gene delivery agents involves polyethylene amines (PEIs). PEIs can condense DNA into nanoscale packages that allow easy cellular uptake. PEIs are potent gene delivery agents due to their pH buffering capacity, allowing PEIs to escape the endosomal barrier avoiding lysosomal degradation. However, the pharmacokinetic properties of PEIs render state of the art PEIs too toxic for clinical applications. PEIs that do not degrade instead accumulate in vivo, resulting in cytotoxicity. Degradation of PEIs may reduce toxicity by allowing for elimination of degraded small molecular weight metabolites through an excretion pathway. Degradation also assists in release of gene cargo being transported by a PEI.
Lower molecular weight PEIs and branched PEIs have lower cytotoxicity as compared to their higher molecular weight PEI counterparts. To promote degradability, small molecular weight PEIs may be cross-linked using degradable cross-linkers. However, incorporating some cross-linkers into a PEI chain may compromise gene delivery efficacy.
PEIs may be linear or branched. As shown in Scheme 1, linear PEIs may be synthesized by ring-opening cationic polymerization of functional, e.g. ethyl functionalized, oxazoline monomers to yield polyoxazolines. Subsequent hydrolysis of the polyamide intermediate yields linear PEIs with terminal amine moieties.
The amine spacing in the PEI product is limited, however, by (1) the number of carbon atoms in the oxazoline ring and (2) the oxazoline ring strain. Furthermore, these polymers tend to be expensive and have limited solubility.
As shown in Scheme 2, branched PEIs may be synthesized by ring-opening polymerization of aziridine monomers.
Depending on the reaction conditions, different degrees of branching may be realized along with terminal amine moieties. As with linear PEIs, the synthesis of branched PEIs is also limited by the number of carbon atoms of the aziridine monomers as well as the ring strain of the aziridine monomers. Branched PEIs are more soluble in a wide range of solvents and less expensive than linear PEIs. However, the large number of terminal amine moieties on branched PEIs renders branched PEIs unfavorably toxic.
Therefore, there is a need in the art for PEI analogs that have maintained or improved efficacy for various applications and, for clinical applications, have favorable toxicity. There is also a need in the art for improved syntheses of polyalkylamines and PEI analogs.